The disclosure of Japanese Patent Application No. 2000-151603 filed on May 23, 2000, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The present invention relates to a fuel supply amount control apparatus and method for a spark ignition type internal combustion engine that is installed as a vehicle-driving engine and that allows a lean combustion based on an air-fuel mixture that has a lower proportion of fuel than a stoichiometric air-fuel ratio mixture, wherein an idling control amount for maintaining a target idle revolution speed during idling is calculated, and wherein if the lean combustion is performed during idling, the amount of fuel supplied is adjusted based on the idling control amount.
2. Description of Related Art
Direct injection internal combustion engines and lean-burn internal combustion engines which improve fuel economy by reducing the pump loss and the heat loss of the spark ignition type internal combustion engines and thereby increasing the theoretical heat efficiency are known. The direct injection type engines, in particular, allow combustion of a very lean mixture by conducting a stratified charge combustion in which an amount of fuel whose proportion to the amount of intake air is less than the fuel-to-intake air proportion represented by a stoichiometric air-fuel ratio is stratified and is ignited. Therefore, even during a low-load and low-speed state of the engine, for example, during an idling state, a large amount of air can be taken in by opening a throttle valve to a great degree, so that the pump loss and the thermal loss can be sufficiently reduced.
Similarly, the lean-burn engines conduct a homogeneous lean combustion in which intake air is homogeneously mixed with an amount of fuel whose proportion to the amount of intake air is less than the fuel-to-intake air proportion represented by a stoichiometric air-fuel ratio and such a homogeneous mixture is ignited. In this case, too, during a low-load and low-speed state of the engine, for example, during idling, a large amount of air can be taken in by opening a throttle valve to a great degree, so that the pump loss and the thermal loss can be reduced.
The aforementioned engine of either one of the direct injection type and the lean-burn type calculates an idling control amount for maintaining the engine revolution speed at a target idle revolution speed through a feedback control of bringing the engine revolution speed to the target idle revolution speed during the idling state. During the idling of the vehicle, the engine performs a fuel injection amount control taking the idling control amount into account, so as to increase the amount of fuel injection in accordance with a request (see, for example, Japanese Patent Application Laid-Open No. 10-169490).
Although the direct injection type engine and the lean-burn type engines are able to reduce the pump loss and the heat loss as described above, it becomes impossible to achieve a sufficient level of generally-termed intake negative pressure, that is, negative pressure in the engine intake passage, when the throttle valve is opened to a great degree during the idling state.
When the intake negative pressure becomes insufficient during the idling state as mentioned above, a problem arises, for example, in a case where intake negative pressure is utilized for a brake booster. In such a case, sufficient amplification of brake pedal-depressing force may become impossible during the idling state. Furthermore, if the amount of intake air is excessively large, the burning rate may be excessively increased, thereby causing a problem of great combustion noises during the idling state, and the like. Therefore, during the idling state, the degree of opening of the throttle valve is kept at a relatively reduced degree to produce a necessary intake negative pressure.
If the running of the vehicle is started from the idling state in which a necessary intake negative pressure is produced as mentioned above, there is no need to reduce the degree of opening of the throttle valve particularly for the sake of the brake booster, reduction of combustion noises, etc. Furthermore, at the time of start of the vehicle, the vehicle running speed is low, and therefore, the vehicle running resistance is small, that is, there is substantially no difference from the idling state where the vehicle running resistance is xe2x80x9c0xe2x80x9d.
Therefore, when the low-speed running of the vehicle is started, the amount of fuel needed to run the vehicle is not clearly different from the amount of fuel consumed during the idling state. That is, the amount of fuel needed at the start of the low-speed running of the vehicle is substantially the same as the amount fuel consumed during the idling state of the engine.
Hence, in a case where an idling control amount is calculated during the idling state and the fuel injection amount control taking the idling control amount into account is performed at the time of running the vehicle as in the conventional art, there is a danger that an increase in the amount of fuel injection achieved in accordance with a fuel increase request may result in an excessively great output torque of the engine so that the stable low-speed running of the vehicle may become difficult.
It is one object of the invention to realize the stable low-speed running of a vehicle equipped with a spark ignition type internal combustion engine that conducts a lean combustion, such as a stratified charge combustion or the like.
In accordance with a first aspect of the invention, a fuel supply amount control apparatus for a spark ignition type internal combustion engine is installed in a vehicle as a vehicle-driving engine and allows a lean combustion of a mixture in which a proportion of fuel is less than in a mixture of a stoichiometric air-fuel ratio. The fuel supply amount control apparatus calculates an idling control amount for keeping a revolution speed of the internal combustion engine at a target idle revolution speed during an idling state of the engine, and adjusts an amount of fuel supplied based on the idling control amount if the lean combustion is conducted during the idling state. The control apparatus also reflects (uses) a control amount obtained by reducing the idling control amount when determining the amount of fuel supplied for the lean combustion during a run of the vehicle.
The control apparatus reflects the control amount obtained through the reducing correction of the idling control amount when determining the amount of fuel supplied for the lean combustion when the vehicle is running. Thus, instead of reflecting the idling control amount for keeping the revolution speed of the engine at the target idle revolution speed immediately in the amount of fuel supplied for the lean combustion during the running of the vehicle, the control apparatus reflects a control amount obtained after the reducing correction of the idling control amount in the aforementioned amount of fuel supplied.
Therefore, during the lean combustion at the time of start of the running of the vehicle, an increase in the amount of fuel injection achieved in accordance with a fuel increase request does not cause an excessive output torque of the engine while the vehicle speed is low, so that the low-speed running of the vehicle becomes stable and good drivability can be maintained.
Furthermore, unnecessary fuel injection is avoided, so that fuel economy improves.
In the above-described aspect of the invention, the control apparatus may reflect the control amount obtained through the reducing correction of the idling control amount performed in accordance with the running speed of the vehicle, in the amount of fuel supplied for the lean combustion during the running of the vehicle.
The vehicle running resistance changes in accordance with the vehicle running speed. Therefore, if the control amount obtained by correcting the idling control amount in the reducing direction in accordance with the vehicle running speed is reflected in the amount of fuel supplied for the lean combustion during the running of the vehicle, an appropriate amount of fuel can be supplied corresponding to the running resistance of the vehicle. Hence, the controllability of the output torque of the engine improves, so that the low-speed running of the vehicle becomes more stable, and better drivability can be maintained.
In the above-described aspect of the invention, the control apparatus may reflect the control amount obtained through the reducing correction of the idling control amount performed in accordance with the revolution speed of the engine, in the amount of fuel supplied for the lean combustion during the running of the vehicle.
The engine efficiency changes in accordance with the engine revolution speed. Therefore, if the control amount obtained by correcting the idling control amount in the reducing direction in accordance with the revolution speed of the engine is reflected in the amount of fuel supplied for the lean combustion during the running of the vehicle, an appropriate amount of fuel can be supplied corresponding to the efficiency of the engine. Hence, the controllability of the output torque of the engine improves, so that the low-speed running of the vehicle becomes more stable, and better drivability can be maintained.
In the above-described aspect of the invention, the fuel supply amount control apparatus may further include a transmission mechanism having a fluidic power transfer mechanism that transfers a drive power between an input shaft and an output shaft via a fluid and that assumes a locked-up state in which the input shaft and the output shaft are interlocked when necessary. When the fluidic power transfer mechanism is in the locked-up state, the control apparatus reflects the control amount obtained through the reducing correction of the idling control amount in the amount of fuel supplied for the lean combustion during the run of the vehicle. When the fluidic power transfer mechanism is in an unlocked state, the control apparatus reflects a control amount set without the reducing correction of the idling control amount or a control amount obtained through a reducing correction of the idling control amount that is performed to a lesser extent than the reducing correction performed during the locked-up state, in the amount of fuel supplied for the lean combustion during the run of the vehicle.
In a vehicle equipped with the transmission mechanism that includes the fluidic power transfer mechanism that selectively assumes the locked-up state, the efficiency in transferring the output torque of the engine is low when the fluidic power transfer mechanism is in the unlocked state. Therefore, during the unlocked state, excessively great output torque of the engine, if any occurs, has only a reduced effect on the state of running of the vehicle. When the fluidic power transfer mechanism is locked up, the engine output torque transfer efficiency improves, so that problems caused by excessively great output torque of the engine become remarkable.
Therefore, when the vehicle is running with the fluidic power transfer mechanism unlocked, the stable low-speed running of the vehicle is maintained even if an excessive amount of fuel is supplied to the engine during the lean combustion mode. Furthermore, due to the fuel increase effect, revolution of the engine is stabilized, and the anti-engine stall characteristic during the low-speed running of the vehicle can be improved. When the vehicle is running with the locked-up state, the vehicle running speed is relatively high, so that a good anti-engine stall characteristic can be maintained even if the amount of fuel supplied is reduced. Furthermore, since the controllability of the output torque of the engine improves, the stable state of the low-speed running of the vehicle continues, and good drivability is maintained.
In the above-described aspect of the invention, the lean combustion may be a stratified charge combustion in which a high-fuel concentration layer is formed by using an amount of fuel whose proportion to an amount of intake air is less than a fuel-to-intake air proportion represented by a stoichiometric air-fuel ratio and the high-fuel concentration layer is ignited.
One example of the lean combustion is the stratified charge combustion in which an amount of fuel whose proportion to the amount of intake air is less than the fuel-to-intake air proportion represented by a stoichiometric air-fuel ratio is stratified with a high fuel concentration and is ignited. During the stratified charge combustion, there is substantially no difference between the amount of fuel supply needed during the idling state and the amount of fuel supply needed during the low-speed running of the vehicle, so that the aforementioned advantages are remarkable.
In the above-described aspect of the invention, the lean combustion may be a homogeneous lean combustion in which a mixture is formed by mixing an amount of intake air with an amount of fuel whose proportion to the amount of intake air is less than a fuel-to-intake air proportion represented by a stoichiometric air-fuel ratio and the mixture is ignited.
Another example of the lean combustion is the homogeneous lean combustion in which a mixture is formed by homogeneously mixing an amount of intake air with an amount of fuel whose proportion to the amount of intake air is less than the fuel-to-intake air proportion represented by a stoichiometric air-fuel ratio and is ignited. During the homogeneous lean combustion, there is substantially no difference between the amount of fuel supply needed during the idling state and the amount of fuel supply needed during the low-speed running of the vehicle, so that the aforementioned advantages are remarkable.